After enduring a sexless marriage, mother-in-law Eri receives a mysterious package. Curious, she opens it to find erotic lingerie and a vibrator inside. A note labeled "free trial" leaves her with no suspicion, and Eri immediately begins using the device. However, this is actually a trap set by her son-in-law, Hidetake, who has long been obsessed with Eri's huge tits and secretly photographed her. Now, he moves in to take advantage of her helpless state—closing in on her body at last.